Since the launch of Sputnik in the 1950s, thousands of satellites have been put into orbit around the Earth and even other planets. Each has served a different purpose, from complex space stations like the International Space Station to the Global Positioning System. Most satellites can be considered to be "in space", but in terms of the Earth's atmosphere, they reside in either the thermosphere or the exosphere. The layer through which a satellite orbits depends on what the satellite is used for and what kind of orbit it has.
The thermosphere is a region of very high temperature that extends from the top of the mesosphere at around 85 kilometers up to 640 kilometers above the Earth's surface. It is called the thermosphere because temperatures can reach up to 1500 degrees Celsius. However, despite the high temperatures, the pressure is too low for objects in this layer to overheat from exposure.
Above the thermosphere is a final layer called the exosphere, which extends up to 10,000 kilometers, or 6,200 miles, above the Earth, depending on how it is defined. Some definitions of the exosphere include all space up until the point where atoms are no longer gravitationally bound to the Earth and get knocked away by solar wind. The upper boundary is difficult to define since the exosphere has no pressure and molecules float freely on ballistic trajectories. Eventually, the exosphere gives way to space outside of the Earth's influence.
Low Earth Orbit
Low Earth Orbit, or LEO, is the lowest orbit in use by satellites and includes any orbit below 2,000 kilometers. Satellites at this altitude circle the Earth very quickly and their orbits degrade faster, which means they will eventually fall back to Earth if not kept up by thrusters. The International Space Station is in LEO and most satellites in LEO fly through the thermosphere, though those at the upper limit of LEO reach into the exosphere. Scientific research satellites are typically put into LEO so they can more closely monitor some type of activity on Earth.
Mid and High Earth Orbit
Satellites above LEO are all orbiting through the exosphere and can maintain their orbits for decades without adjustment. Weather and communication satellites are found in higher orbits because they need longer views of a given area of the planet to either carry transmissions or record data. At the top of High Earth Orbit is geosynchronous orbit. Any satellite here will have an orbital period the same as the Earth's. A special version of the geosynchronous orbit is the geostationary orbit, which is the same but is along the equator. This keeps the satellite at the same point in the sky throughout the entire orbit.